C# – How to deterministically dispose of a managed C++/CLI object from C#

cc++-cliinterop

I have a managed object in a C++/CLI assembly. Being C++/CLI, it implements the Disposable pattern through its "destructor" (yes, I'm aware it's not the same as a standard C++ destructor). From C++/CLI, I would simply delete the object. However, I am using this object as a member variable in a C# class.

From my C# class, then, I would like to call the equivalent of the Dispose() method on the C++/CLI object when I am finished using it. Since it is (and must be) a member variable of the class, utilizing a using() block is out of the question. As far as I can tell, there is no exposed method for direct, deterministic disposal of resources from a language other than C++/CLI. How can I accomplish this?

Best Answer

It is not so obvious in C++/CLI but it works exactly the way it does in C#. You can see it when you look at the class with Object Browser. Or a decompiler like ildasm.exe, best way to see what it does.

When you write the destructor then the C++/CLI compiler auto-generates a bunch of code. It implements the disposable pattern, your class automatically implements IDisposable, even though you didn't declare it that way. And you get a public Dispose() method, a protected Dispose(bool) method and an automatic call to GC::SuppressFinalize().

You use delete in C++/CLI to explicitly invoke it, the compiler emits a Dispose() call. And you get the equivalent of RAII in C++/CLI by using stack semantics, the compiler automatically emits the Dispose call at the end of the scope block. Syntax and behavior that's familiar to C++ programmers.

You do the exact same thing you'd do in C# if the class would have been written in C#. You call Dispose() to invoke explicitly, you use the using statement to invoke it implicitly in an exception-safe way.

Same rules apply otherwise, you only need the destructor when you need to release something that is not managed memory. Almost always a native object, the one you allocated in the constructor. Consider that it might not be worth the bother if that unmanaged object is small and that GC::AddMemoryPressure() is a very decent alternative. You do however have to implement the finalizer (!ClassName()) in such a wrapper class. You cannot force external client code to call Dispose(), doing so is optional and it is often forgotten. You don't want such an oversight to cause an unmanaged memory leak, the finalizer ensures that it is still released. Usually the simplest way to write the destructor is to explicitly call the finalizer (this->!ClassName();)

Related Solutions

Ruby – How to call shell commands from Ruby

This explanation is based on a commented Ruby script from a friend of mine. If you want to improve the script, feel free to update it at the link.

First, note that when Ruby calls out to a shell, it typically calls /bin/sh, not Bash. Some Bash syntax is not supported by /bin/sh on all systems.

Here are ways to execute a shell script:

cmd = "echo 'hi'" # Sample string that can be used

Kernel#` , commonly called backticks – `cmd`

This is like many other languages, including Bash, PHP, and Perl.

Returns the result (i.e. standard output) of the shell command.

Docs: http://ruby-doc.org/core/Kernel.html#method-i-60
```
value = `echo 'hi'`
value = `#{cmd}`
```
Built-in syntax, %x( cmd )

Following the x character is a delimiter, which can be any character. If the delimiter is one of the characters (, [, {, or <, the literal consists of the characters up to the matching closing delimiter, taking account of nested delimiter pairs. For all other delimiters, the literal comprises the characters up to the next occurrence of the delimiter character. String interpolation #{ ... } is allowed.

Returns the result (i.e. standard output) of the shell command, just like the backticks.

Docs: https://docs.ruby-lang.org/en/master/syntax/literals_rdoc.html#label-Percent+Strings
```
value = %x( echo 'hi' )
value = %x[ #{cmd} ]
```
Kernel#system

Executes the given command in a subshell.

Returns true if the command was found and run successfully, false otherwise.

Docs: http://ruby-doc.org/core/Kernel.html#method-i-system
```
wasGood = system( "echo 'hi'" )
wasGood = system( cmd )
```
Kernel#exec

Replaces the current process by running the given external command.

Returns none, the current process is replaced and never continues.

Docs: http://ruby-doc.org/core/Kernel.html#method-i-exec
```
exec( "echo 'hi'" )
exec( cmd ) # Note: this will never be reached because of the line above
```

Here's some extra advice: $?, which is the same as $CHILD_STATUS, accesses the status of the last system executed command if you use the backticks, system() or %x{}. You can then access the exitstatus and pid properties:

$?.exitstatus

For more reading see:

C# – How to cast int to enum

From an int:

YourEnum foo = (YourEnum)yourInt;

From a string:

YourEnum foo = (YourEnum) Enum.Parse(typeof(YourEnum), yourString);

// The foo.ToString().Contains(",") check is necessary for enumerations marked with an [Flags] attribute
if (!Enum.IsDefined(typeof(YourEnum), foo) && !foo.ToString().Contains(","))
{
    throw new InvalidOperationException($"{yourString} is not an underlying value of the YourEnum enumeration.")
}

Update:

From number you can also

YourEnum foo = (YourEnum)Enum.ToObject(typeof(YourEnum) , yourInt);

Best Answer

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Ruby – How to call shell commands from Ruby

C# – How to cast int to enum

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